Objects in classical physics are in a well defined state. In quantum physics a particle exists in general in several states simultaneously – it is not in a definite state. For example, in classical physics an object spins either clockwise or counterclockwise and around a definite axis. In quantum physics, an electron may spin simultaneously in both directions and around any possible axis there is. In other words, a particle concurrently spins around any probable state that is possible. Erwin Schrödinger, one of the founders of quantum physics, drew the analogy of a cat being dead and alive at the same time. The cat is put in a closed box with a bottle of poison gas and a radioactive particle. If the particle decays it triggers a hammer to smash the bottle. The poison is released and the cat dies. At any time before it is observed the cat may be dead or alive. We cannot be certain which it is until we open the box but in quantum mechanics, the cat can exist in a combination of live and dead states. This simultaneous existence in different states is called superposition of states. According to quantum theory, the superposition remains till we open the box. As soon as we open the door we just see one outcome (either a dead or a live cat). This implies to any other object and to the objective reality in its totality. Before we observe it, the reality a superposition of states.
This superposition of states is expressed in the wave equation that describes the state of the particle (or cat). The wavefunction includes components that describe all possible states of the particle (or cat).